1. Field of the Invention
The present invention relates to a laser processing method and apparatus for applying a pulsed laser beam to a workpiece formed from a transparent member, thereby performing laser processing to the workpiece.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer formed from a silicon substrate to thereby partition a plurality of regions where circuits such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the regions where the circuits are formed from each other, thus obtaining individual semiconductor chips. Further, an optical device wafer is provided by forming gallium nitride compound semiconductor or the like on the front side of a substrate such as a sapphire substrate, silicon carbide substrate, silicon dioxide substrate, lithium tantalate substrate, and lithium niobate substrate. The optical device wafer is also cut along the streets to obtain individual optical devices divided from each other, such as light emitting diodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer along the streets, there has recently been proposed a method including the steps of applying a pulsed laser beam having an absorption wavelength (e.g., 532 nm, 355 nm, 266 nm) to the wafer along the streets to thereby form laser processed grooves on the wafer along the streets by ablation and next breaking the wafer along the laser processed grooves (see Japanese Patent Laid-open No. 2005-353935, for example).